Measurement of catecholamines, met-enkephalin, somatostatin and substance P-like immunoreactivities in 12 human pheochromocytomas

Pheochromocytomas and Paragangliomas as Causes of Endocrine Hypertension

Chromaffin tumors are included among the causes of secondary hypertension because of the release of catecholamines. Nevertheless, the clinical, cardiovascular, and hypertensive picture of patients affected by pheochromocytomas/paragangliomas (PPGL) is extremely variable, due to the different quantitative and qualitative releasing activity of these tumors. A consistent percentage of these patients, about 20%, is normotensive and not affected by the characteristic symptomatic crises due to sudden release of catecholamines. The factors causing such wide clinical variability are many and probably not all known. It is well known that many of these tumors are genetically determined and that the genetic profile influences the biochemical characteristics and the biology of the tumors as well as the clinical presentation of the affected patients. The number of asymptomatic or poorly symptomatic patients is increased after the introduction of genetic screening and the early diagnosis in mutation carriers. In this paper we can review the genotype-phenotype correlation of PPGLs with a focus on the cardiovascular picture.

Subclinical phaeochromocytoma

Phaeochromocytomas and paragangliomas are neural crest-derived tumours. Autopsy studies indicate that relatively large numbers of these tumours remain undiagnosed during life. This may reflect non-specific signs and symptoms and low medical alertness in evaluating the clinical picture or it may reflect a silent clinical presentation - the subclinical phaeochromocytoma. The associated clinical picture depends on the capacity of the tumours to release catecholamines and sometimes biologically active peptides. Hypertension is the hallmark of catecholamine release, but the amount, type and pattern of catecholamine secretion is extremely variable. Some tumours have low or intermittent secretory activity, some produce mainly or solely dopamine, while others very rarely do not synthesize or release any catecholamines (non-secretory or non-functional tumours). Such tumours may present with mild or even absent signs and symptoms of catecholamine excess. Low secretory activity may reflect small tumour size or differences in secretory phenotypes associated with the biochemical and genetic background of the tumours. Tumours due to succinate dehydrogenase subunit B mutations are often subclinical, poorly differentiated, contain low amounts of catecholamines, and are usually malignant at diagnosis. Adrenoceptor desensitization can result in a subclinical presentation, even when catecholamine levels are high. Subclinical phaeochromocytomas are often discovered as incidentalomas during radiological procedures or during routine screening for phaeochromocytoma in carriers of mutations in one of the ten currently identified tumour susceptibility genes. Undiagnosed phaeochromocytomas, whether or not subclinical and even if biologically benign, may cause extremely deleterious consequences or even death, following abrupt release of catecholamines.

Immunohistochemical evaluation of a malignant phecochromocytoma in a wolfdog

A malignant pheochromocytoma with multiple metastases was diagnosed in a 7-year-old male wolfdog that resulted from a cross between an eastern timber wolf (Canis lupus lycaon) and an Alaskan malamute. A yellowish white neoplastic mass approximately 10 cm diameter was found in the right adrenal gland. The neoplasm penetrated through the wall of the caudal vena cava. A diagnosis of pheochromocytoma was established by histopathologic and immunohistochemical procedures. Immunohistochemically, the neoplastic cells expressed chromogranin A, substance P, synaptophysin, Leu-7, protein gene product 9.5, methionine-enkephalin, S100 protein, and galanin. Multiple metastatic tumors were found in the kidneys, spleen, lungs, heart, and liver.

Neuropeptides in the sympathetic system: presence, plasticity, modulation, and implications

Neuropeptides are ubiquitous in the sympathetic system and modulate transmission at the levels of the intermediolateral cell column, sympathetic ganglia, and neuroeffector junctions. Several neuropeptide-containing pathways from the hypothalamus and medulla modulate excitability of preganglionic neurons. Neuropeptides coexist with norepinephrine or acetylcholine in subpopulations of chemically coded, target-specific sympathetic ganglion neurons. Neuropeptide Y is colocalized in adrenergic vasoconstrictor neurons, whereas vasoactive intestinal polypeptide is colocalized in cholinergic sudomotor neurons. Neuropeptide expression is plastic; during development, neurons that switch from a noradrenergic to a cholinergic phenotype increase expression of vasoactive intestinal polypeptide, somatostatin, and substance P. Preganglionic inputs increase neuropeptide Y and inhibit substance P expression. Sympathetic denervation produces sprouting of sensory fibers containing substance P and calcitonin gene-related peptide in target tissues. Neuropeptides from preganglionic fibers (e.g., enkephalin) and primary afferents (e.g., substance P, vasoactive intestinal polypeptide) modulate transmission in sympathetic ganglia. Neuropeptide Y produces vasoconstriction, prejunctional inhibition of norepinephrine release, and postjunctional potentiation of norepinephrine effects. Plasma neuropeptide Y increases during intense sympathoexcitation, hypertension, and pheochromocytoma. Dystrophic neurites containing neuropeptide Y occur in human sympathetic ganglia during aging, diabetes, and dysautonomia. Sympathetic neuropeptides may thus have important clinical implications.

Augmented enkephalin-immunoreactivity in adrenaline-producing phaeochromocytomas

Immunohistochemical studies for methionine- and leucine-enkephalin were performed on 26 phaeochromocytomas to elucidate the patho-physiological roles of enkephalins. Positive reactions were seen in all phaeochromocytomas with varying intensities. The location of methionine- and leucine-enkephalin agreed fairly well with each other. Stronger immunostaining was obtained in phaeochromocytomas secreting both adrenalin and noradrenaline than in those secreting predominantly noradrenaline. Paroxysmal hypertension was frequently observed in patients with adrenalin-secreting phaeochromocytomas, especially those with marked enkephalin positivity. Urinary excretion of metanephrine was significantly correlated with enkephalin positivity. These findings show that all phaeochromocytomas retain the ability to produce enkephalins of the adreno-medullary or extra-medullary chromaffin tissues from which they derive. Augmented enkephalin-immunoreactivity in adrenalin-producing phaeochromocytomas may be interpreted as reflecting a close association of enkephalins with adrenalin under physiological conditions.